Field of the Invention
Embodiments of the present invention relate generally to a blanking device for multi charged particle beams, a multi charged particle beam writing apparatus, and a method for blocking defective beams of multi charged particle beams, and more specifically, to a blanking device used in multi-beam writing and a method for blocking defective beams by using the blanking device, for example.
Description of Related Art
The lithography technology that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are generated in semiconductor manufacturing. In recent years, with high integration of LSI, the linewidth (critical dimension) required for semiconductor device circuits is decreasing year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” a mask pattern on a mask blank with electron beams.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time (one shot) in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multi-beams are formed by letting portions of an electron beam emitted from an electron gun assembly pass through a corresponding hole of a plurality of holes in the mask, blanking control is provided for each of the beams, and each unblocked beam is diminished by an optical system to reduce a mask image, and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is separately controlled based on an irradiation time. For highly accurately controlling such a dose of each beam, it is necessary to perform high speed blanking control to provide an ON or OFF state of each beam. In a writing apparatus of a multi-beam system, a blanking control circuit for each beam is placed on a blanking plate where blankers each for each of multi-beams are arranged.
Here, each blanker for the multi-beams is configured by a pair of counter electrodes, and specifically, a voltage for blanking control is applied to a control electrode and the other counter electrode is grounded. In blanking control, a beam OFF state is generated for the grounded counter electrode by applying a positive potential to the control electrode in order to deflect a beam toward the control electrode so as not to let the beam pass through a limiting aperture of the blanking aperture member. For example, when multi-beams are composed of n×n beams, n×n pairs of electrodes and their control circuits are arrayed in the blanking device. For example, with respect to a blanking device in which 512×512 pairs of electrodes and their control circuits are arrayed, it is reported that the fraction defective of the structure that is configured by the 512×512 pairs of electrodes and their control circuits is about 0.04%. As one of defects, there is a case in which the potential of the control electrode is fixed to a ground potential by some malfunction. In such a case, since the electric potential of the counter electrode is a ground potential, no electric field is generated between the electrodes, thereby not deflecting beams. Accordingly, beams are not controlled to be beam OFF. Then, such uncontrolled beams being fixed to beam ON pass through a limiting aperture. There arises a problem that writing defect occurs because such unwanted beams irradiate the target object. Such configuration defects caused by pairs of electrodes and their control circuits may be produced at the stage of fabrication or produced with a high probability by a failure during use after mounting them in the writing apparatus. It is conventionally difficult to check the beam control state before actually placing them in the writing apparatus and emitting each beam of the multi-beams. Although defects produced at the stage of fabrication can be detected by inspection after the fabrication, if a defect being fixed to beam ON occurs during used for writing processing, the blanking device comes to be unusable thereafter.
Conventionally, a method is examined in which, before beams including such a defective beam being fixed to beam ON irradiate the target object, a movable block member is transferred to be directly underneath the beams in order to compulsorily perform blocking (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2013-128031).